The human spine is a column of articulating vertebrae separated by intervertebral discs. It provides support for the torso, and houses and protects the spinal cord in its spinal canal.
The human intervertebral disc is an oval-shaped to kidney-shaped structure of variable size depending on its location in the spine. The outer portion of the disc is known as the annulus fibrosus (or anulus fibrosus, annulus fibrosis, anulus fibrosis) or simply “the annulus”. The inner portion of the disc is known as the nucleus pulposis or simply “the nucleus”.
The annulus is made up of ten to twenty collagen fiber lamellae. The collagen fibers within a given lamella extend parallel to one another. Successive lamellae have their collagen fibers oriented in alternating directions. About 48 percent of the lamellae are incomplete, but this percentage varies with location and it increases with age. On average, the collagen fibers of a given lamella lie at an angle of about sixty degrees to the vertebral axis line, but this too varies with location. The orientations of the lamellae serve to control vertebral motion (i.e., one half of the lamellae tighten to check motion when the vertebra above or below the disc are turned in either direction).
The annulus contains the nucleus. The nucleus has a consistency generally similar to that of crabmeat. The nucleus serves to transmit and dampen axial loads. A high water content (approximately 70-80 percent) assists the nucleus in this function. The water content has a diurnal variation. The nucleus absorbs water while a person lies recumbent. Activity generates increased axial loads which squeeze water from the disc. The nucleus comprises roughly 50 percent of the entire disc. The nucleus contains cells (chondrocytes and fibrocytes) and proteoglycans (chondroitin sulfate and keratin sulfate). The cell density in the nucleus is on the order of 4,000 cells per microliter.
The intervertebral disc changes, or “degenerates”, with age. As a person ages, the water content of the disc falls from approximately 85 percent at birth to approximately 70 percent in the elderly. The ratio of chondroitin sulfate to keratin sulfate decreases with age, while the ratio of chondroitin 6 sulfate to chondroitin 4 sulfate increases with age. The distinction between the annulus and the nucleus decreases with age. Generally, disc degeneration is painless.
Premature or accelerated disc degeneration is known as degenerative disc disease. A large portion of patients suffering from chronic lower back pain are thought to have this condition. As the disc degenerates, the nucleus and annulus functions are compromised. The nucleus becomes thinner and less able to handle compressive loads. The annulus fibers become redundant as the nucleus shrinks. The redundant annular fibers are less effective in controlling vertebral motion. This disc pathology can result in (i) tears of the annulus (both “full-thickness” tears and “partial-thickness” tears) as abnormal loads are transmitted to the annulus and the annulus is subjected to excessive motion between vertebrae, and (ii) disc herniation (i.e., extrusion of the nucleus) through complete (i.e., full-thickness) annular tears. Degenerative disc disease is frequently the cause of substantial pain for a patient.
Current surgical treatments for disc degeneration are generally “destructive”, in the sense that they generally involve the removal or destruction of disc tissue.
One group of procedures, which includes microlumbar discectomy, removes the nucleus or a portion of the nucleus.
A second group of procedures destroys nuclear material. This group includes Chymopapin (an enzyme) injection, laser discectomy, and thermal therapy (i.e., heat treatment to denature proteins in the nucleus).
The foregoing two groups of procedures compromise the nucleus of the treated disc, and may exacerbate fissures in the annulus while accessing the nucleus.
A third group of procedures, which includes spinal fusion procedures, either removes the disc or effectively eliminates the disc's function by connecting together two or more vertebrae, e.g., by “fusing” the vertebrae together with bone. However, such spinal fusion procedures transmit additional stress to the adjacent discs, which typically results in premature degeneration of the adjacent discs over time.
In general, the “destructive” nature of current surgical treatments for disc degeneration can provide substantial pain relief for the patient, but it can also lead to further disc degeneration over time, which can result in new pain for the patient. By way of example but not limitation, procedures to remove the nucleus or a portion of the nucleus, and procedures to destroy nuclear material, compromise nucleus function and may exacerbate fissures in the annulus while accessing the nucleus, thereby leading to further disc degeneration. By way of further example but not limitation, spinal fusion procedures can induce premature disc degeneration in adjacent intervertebral discs.
Ideally, disc herniation (i.e., the extrusion of nucleus through full-thickness annular tears) should be treated by closing the fissures in the annulus. However, in practice, this is difficult to achieve.
By way of example but not limitation, it is difficult to close fissures in the annulus by conventional suturing. For one thing, the annulus is tough and thick and does not lend itself to manual suturing, particularly given the limited access corridors often imposed on the surgeon. For another thing, the loads imposed on the nucleus are large, so that inadequate closure of the fissures can lead to subsequent recurrence of the fissures. Furthermore, the area surrounding the intervertebral disc is crowded with delicate structures (e.g., nerves), so that the use of knots to secure suture can be problematic.
By way of further example but not limitation, it is difficult to close fissures in the annulus using conventional toggle anchors. More particularly, in U.S. Pat. No. 7,004,970, issued Feb. 28, 2006 to Cauthen III et al., there is disclosed a system for closing fissures in the annulus, wherein the system comprises first and second conventional toggle anchors connected together by filament, and wherein the filament comprises a cinch knot and a cinch line. See, for example, FIGS. 61A, 61B, 62A-62D and 63 of Cauthen III et al. With this system, the first conventional toggle anchor is passed through the annulus and into the nucleus on a first side of a fissure, the second conventional toggle anchor is passed through the annulus and into the nucleus on a second side of the fissure, and then the cinch line is pulled to draw together the two conventional toggle anchors and thereby close the fissure. However, this system suffers from significant drawbacks. First, it is difficult to reliably toggle conventional toggle anchors within the nucleus, which can result in poor setting of the conventional toggle anchors within the intervertebral disc and hence inadequate closure of the fissure. Second, it is difficult to set the cinch knot close to the surface of the annulus, particularly given the limited access corridors often imposed on the surgeon, which can result in inadequate closure of the fissure and interference with the delicate structures around the intervertebral disc, e.g., nerves, etc. Third, the cinch knot can easily slip, thereby undermining the closure of the fissure. For this reason, systems using conventional toggle anchors have achieved limited success in closing fissures within the annulus.
In Cauthen III et al., there is also disclosed a knotless system for tensioning the filament between the two conventional toggle anchors, wherein enlargements are formed on the filament and are pulled through a narrow opening formed on one of the conventional toggle anchors so as to provide a knotless ratchet securement. However, this knotless ratchet securement is limited to preset tension levels (i.e., it is not continuously adjustable) and has limited holding power, among other things.
Thus there is a need for a new and improved method and apparatus for closing fissures in the annulus of an intervertebral disc, whereby to treat degenerative disc disease.
In addition to the foregoing, in many other situations it may be necessary and/or desirable to effect anatomical repairs and/or fixations.
By way of example but not limitation, two pieces of soft tissue may need to be held in apposition to one another to effect a repair (e.g., so as to close an incision in the skin), or two pieces of cartilage may need to be held in apposition to one another to effect a repair (e.g., so as to close a tear in meniscal cartilage), or two pieces of bone may need to be held in apposition to one another so as to effect a repair (e.g., so as to fuse together bone).
By way of further example but not limitation, a piece of soft tissue may need to be held in apposition to bone to effect a repair (e.g., so as to attach soft tissue to bone), or a piece of cartilage may need to be held in apposition to bone to effect a repair (e.g., so as to attach labrum to bone or to attach meniscal cartilage to bone).
By way of further example but not limitation, a prosthesis may need to be held in apposition to soft tissue or bone, or soft tissue or bone may need to be held in apposition to a prosthesis, and/or any first object may need to be held in apposition to any second object.
In these and other situations, it would also be advantageous to provide a new and improved method and apparatus for effecting anatomical repairs and/or fixations.